The invention relates to a delivery unit for fuel having a side channel pump in a housing having a pump chamber and an impeller included in the pump chamber.
In a known delivery unit of this type for delivering fuel from a fuel tank to an internal combustion engine of a motor vehicle (International Patent Disclosure W 095/25885), the feed pump and electric motor for driving it are disposed side-by-side in a housing. The pump wheel or impeller, which is equipped with vanes or impeller blades on its circumference, is seated in a manner fixed against relative rotation on a shaft of the rotor or impeller, which has a rotor or armature winding placed in slots and which revolves in a stator equipped with permanent magnet segments. The supply of current to the armature winding is effected via a commutator or current inverter seated on the rotor shaft and two current brushes resting radially with spring pressure on the commutator.
The delivery unit for fuel according to the invention has the advantage that by combining the rotating parts of the delivery unit, that is, the impeller of the feed pump and rotor of the electric motor, into a single part, a very simple compact construction that can be made at little production cost. In particular, the delivery unit can be quite flat, or in other words can have an extremely small axial dimension. The outer diameter of the delivery unit that is accordingly larger is not only no disadvantage in conjunction with the usual embodiment of the delivery unit but in fact opens up the possibility of additional provisions for improving the efficiency of the delivery unit. By eliminating the commutator and current brushes, brush wear is not a factor, and the service life of the delivery unit is accordingly increased. If the electric motor is embodied as a DC motor, the necessary commutation of the current is done electronically in the stator winding.
In accordance with a preferred embodiment of the invention, the cylindrical pump chamber is defined by two radially extending, axially spaced-apart side walls and a peripheral wall joining the two side walls together along their circular periphery. The impeller faces the side walls with gap clearance, and the inside face of the stator, formed by a slotted lamination packet, forms the peripheral wall of the pump chamber. The impeller has many radial impeller blades, spaced circumferentially apart from one another and between them defining axially open blade chambers; the blades are joined together by an outer ring. The permanent magnets are secured to the outer ring and are preferably made of plastoferrites, if the delivery unit is made of plastic.
As an alternative to this, plastic-bonded rare-earth magnets can be used that are preferably embedded in the plastic matrix of the impeller.
In an advantageous embodiment of the invention, a slot-like side wall open toward the pump chamber is embodied in each side wall of the pump chamber, concentrically to the impeller axis, with an interrupting rib remaining between the end and the beginning of the side channel in terms of the flow direction. The beginning of at least one side channel communicates with an intake opening, and the end of the side channel communicates with a pressure outlet; the axes of the inflow and outflow channels are oriented either axially or preferably radially from the intake opening and to the pressure outlet. Because of the especially advantageous radial inflow and outflow of fuel into and out of the pump chamber, a substantial reduction in flow losses is attained, and the pump efficiency is thus improved. The radial oncoming and outgoing flow, in contrast to conventional side channel pumps, is possible without difficulty because of the increased diameter of the delivery unit attained by the construction according to the invention, since as a result there is enough installation space in the radial direction to accommodate suitable inflow and outflow channels.